JERUSALEM — Israel decided to resume pinpoint attacks against Palestinian Arab rocket-launching cells yesterday, hours after two Israeli teenagers were seriously wounded in an attack in a border town, jeopardizing an already shaky, month-old truce.

The boys were wounded in the rocket attack on Sderot, a southern Israeli town near the Gaza border. Shortly after the new policy was announced, a rocket was fired from Gaza but no injuries were reported.

Although Israel said it remains committed to the truce, the decision to strike against rocket launchers raises tensions.

It also could undermine Prime Minister Olmert’s recent efforts to bolster the moderate Palestinian Arab president, Mahmoud Abbas, who is in a standoff with Hamas. The Islamic militant group controls the Palestinian Arab parliament and Cabinet.

“The defense establishment has been instructed to take pinpoint action against the rocket-launching cells,” Mr. Olmert’s office said after a meeting of senior officials. “At the same time, Israel will continue to abide by the ceasefire.”

A Hamas government spokesman, Ghazi Hamad, denounced the Israeli decision to “continue their aggression.”

But he added, “We still believe that this agreement is alive, and both sides should respect this agreement because it is [in] the interest [of] our people.”

Palestinian Arab militants violated the truce within an hour after it took effect on November 26, and by the military’s count, have launched more than 60 rockets at southern Israel since then.

Israel has refrained from responding, but Mr. Olmert had warned in recent days that his patience was wearing thin. Mr. Olmert has come under intense pressure from residents of Sderot, political opponents, and members of his own Cabinet to take action.

The army said the rocket fired yesterday landed in Palestinian Arab territory, but Israel Radio said it landed in an open field in Sderot, causing no injuries or damage. Islamic Jihad militants claimed responsibility.

Most of the crude weapons have been launched by Islamic Jihad, an Iranian-backed radical group that does not participate in Palestinian politics.

An Islamic Jihad spokesman, Abu Hamza, said the group was not moved by Mr. Olmert’s threat.

“Any harm to our leaders will be met with a harsh response,” he said. Mr. Hamza said the rocket fire was a response to Israeli arrests of militants in the West Bank, which is not covered by the truce.

The truce ended five months of deadly fighting that followed an attack by Hamas-linked gunmen on an Israeli army post just outside Gaza. Two soldiers were killed and another was captured in that raid, and Israel retaliated by sending ground troops, artillery, and aircraft to strike at militants and their rocket squads.